Secondarytables或OnetoOne关联? [英] Secondarytables or OnetoOne associations?

问题描述

考虑以下模型":

USER
    Long: PK
    String: firstName
    String: lastName

USER_EXT
    Long: PK
    String: moreInfo
    Date: lastModified

我正在尝试查找/创建正确的Hibernate映射(使用注释)，以便使用像"from User"这样的HQL查询，它会生成以下SQL:

I'm trying to find/create the correct Hibernate mapping (using Annotations) such that, with an HQL query as simple as "from User", it would generate the following SQL:

select firstName, moreInfo from USER, USER_EXT where user.pk = user_ext.pk

我已经尝试了一切，从使用@Secondarytable到@OneToOne关联，但我无法使其正常工作.

I've tried everything, from using @Secondarytable to @OneToOne association, but I can't make it work.

我现在最好的结果是使用@OneToOne关联，该关联会生成多个SQL查询，一个查询用于获取USER中的行，并为结果集中的每一行从USER_EXT中选择查询.

The best result I have now is with the @OneToOne association which generate multiple SQL queries, one to fetch rows in USER and for each rows in the resultset a select query from USER_EXT.

这是无效的.

有什么主意吗?

推荐答案

在OneToOne和Secondarytable之间进行选择在某种程度上取决于对象模型(即，是否要为用户扩展名提供实体).我选择使用OneToOne关联和两个实体.

Choosing between OneToOne and Secondarytable somehow depends on the object model (i.e. if you want an entity for the user extension). I chose to use a OneToOne association and two entities.

对于User(请注意将PrimaryKeyJoinColumn用于共享主键):

For the User (note the use of the PrimaryKeyJoinColumn for the shared primary key):

@Entity
public class User {

    @Id private Long id;
    private String firstName;
    private String lastName;

    @OneToOne
    @PrimaryKeyJoinColumn
    private UserExt userExt;

    public UserExt getUserExt() {
        return userExt;
    }
    public void setUserExt(UserExt userExt) {
        this.userExt = userExt;
    }
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
}

和UserExt:

@Entity
public class UserExt {

    @Id private Long id;
    private String moreInfo;
    @Temporal(TemporalType.DATE)
    private Date lastModified;
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getMoreInfo() {
        return moreInfo;
    }
    public void setMoreInfo(String moreInfo) {
        this.moreInfo = moreInfo;
    }
    public Date getLastModified() {
        return lastModified;
    }
    public void setLastModified(Date lastModified) {
        this.lastModified = lastModified;
    }   
}

使用上述实体，可以进行以下HQL查询:

With the above entities, the following HQL query:

select u.firstName, u.userExt.moreInfo from User u

生成以下SQL查询:

select
  userx0_.firstName as col_0_0_,
  userextx1_.moreInfo as col_1_0_ 
 from
  User userx0_,
  UserExt userextx1_ 
 where
  userx0_.id=userextx1_.id

这是预期的结果.

PS:JPA 1.0实际上不能很好地支持派生标识符(JPA 2.0中的情况要好得多)，除非您使用特定于Hibernate的foreign生成器，否则您必须在UserExt上手动设置Id. .有关详细信息，请参见下面的问题.

PS: JPA 1.0 actually provides poor support of derived identifiers (things are much better in JPA 2.0) and you will have to set the Id manually on the UserExt, unless you use an Hibernate specific foreign generator. See the question below for details.

• JPA Hibernate一对一关系

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